The reduced pressure in such system is conventionally used to primarily transport refuse from one or more toilet bowls into a refuse collection tank. Such systems must be operable, especially during cruising flight when there is a pressure gradient between the space inside the aircraft body or cabin and the environment.
German Patent Publication (DE-OS) 3,026,763 (Badger et al.), published on Feb. 12, 1981, discloses a vacuum toilet flush system. Incidentally, the German Serial Number 3,026,763 is based on U.S. Ser. No. 58,586, filed in the United States of America on Jul. 18, 1979. In said publication a vacuum is produced either by the environment of the aircraft due to the pressure gradient, or by a vacuum pump. The vacuum provides the force for transporting the refuse to a collection tank system. The vacuum air pump mentioned in the reference is for practical purposes an electrically driven blower which is primarily operated when the aircraft is on the ground, because on the ground the mentioned pressure gradient is not available.
Such a blower has a relatively low efficiency, thereby causing a high energy consumption primarily caused by the high starting currents and operating currents. Keeping these currents within acceptable limits requires in turn an installation that is expensive and adds to the overall weight of the aircraft. Due to the high operational r.p.m. of such blowers, special precautions must be taken for avoiding disadvantages of such blowers. Such blowers are a source of nuisance noise and vibrations. In order to protect the blower against contamination, it is arranged downstream of the refuse collection tank which thus must be strong enough to be safe against implosions. Further, the pressure gradient existing during cruising flight is higher than required for the conveying of the refuse. As a result, the operation of a toilet in such a system involves a high noise level at the toilet inlets and a high air volume consumption. In case of small aircraft, the operation of the toilet in such a system may even cause fluctuations in the cabin pressure.
U.S. Pat. No. 3,995,328 (Carolan et al.), issued on Dec. 7, 1976, shows a vacuum toilet for an aircraft, wherein the collecting tank (40) is connected to two air vacuum pumps (50) and (51) through a water separator (49). Two vacuum suction pumps (50, 51) are connected in parallel with each other, presumably because one pump is insufficient to sustain the required vacuum on both sides of the filter (55) in the chambers (40A) and (40B) of the tank (40). Using such large volume air blowers is undesirable, not only because these blowers are noisy, they also cause undesirable vibrations and use up a substantial amount of power for transporting a sufficient volume of air while the aircraft is on the ground or at low altitudes. At high altitudes the reduced ambient pressure is used to maintain the required vacuum in the system of Carolan et al.
U.S. Pat. No. 4,199,828 (Hellers) issued on Apr. 29, 1990 shows a pneumatic ejector for producing the required vacuum in a toilet, for example, on a bus or train. Such a pneumatic ejector requires for its operation a compressed air reservoir (5) readily available on a bus or train from the respective brake system. The use of a pneumatic ejector (2) of Hellers instead of the vacuum suction pumps in Carolan et al. does not make sense, because the ejector of Hellers needs a source of compressed air for its operation. Besides, Hellers does not teach nor suggest passing the waste water directly through the ejector.